In the past, in sorting bearings such as needle bearings, ball bearings or roller bearings, they were allowed to slide down between rotating cylinders whose axes were mounted in a diverging manner so as to provide a gradually enlarging sorting gap between the cylinders. As the bearings slid down the cylinders, they would drop through the gap at the point where the width of the gap exceeded the diameter of the bearings. If it had been possible to make the sorting cylinders perfectly cylindrical, they could be driven while still maintaining the desired sorting gap. However, it is substantially impossible to make a perfectly cylindrical roll and, accordingly, while the variances may not be noticeable to the human eye, when sorting bearings to high tolerances such as ten millionths of an inch, any variance in the diameter of the cylinders causes changes in the width of the sorting gap.
In U.S. Pat. No. 4,172,527, applicant has patented a bearing sorting device which will reliably sort round bearings to tolerances of ten millionths of an inch. In the apparatus disclosed in this patent, a pair of elongated cylinders are rotatably and floatingly supported so that the longitudinal axes of the cylinders diverge, forming a sorting gap between the surfaces of the cylinders. The cylinders are carried on an incline with a drive connected to one end of each of the cylinders for rotating the cylinders in opposite directions. The lower end of the cylinders are connected by timing gears while positively synchronizing the rotation of the cylinders relative to each other so that the same points on the cylinders appear at the sorting gap on each revolution of the cylinders. The bearings which are sorted are fed onto the cylinders at the upper end and moved down the sorting gap until the width of the sorting gap is sufficient to permit the bearings to drop through into predetermined receptacles. The device shown and illustrated in this patent works quite well to sort bearings within ten millionths of an inch. However, it has been found that where the sorting cylinders are driven through a direct driven pulley mechanism, the forces imparted by the driving belt cause a radial deflection of the elongated sorting rolls themselves which causes the sorting gap between the cylinders to vary. Such deflection affects the accuracy of the sorting of the bearings. Looking at FIG. 2 of U.S. Pat. No. 4,172,527, if the drive belts for driving the pulley were perfect, there would be no problem. However, it has been determined that there are always variances in the thicknesses of the drive belts and that this variance in the thickness of the drive belts causes a variance in radial stresses applied to the axle of the sorting cylinders, and to the cylinders themselves as they are rotating.